1. Field of Invention
This invention relates to the determination of air quality as related to acidic precipitation and/or condensation.
2. Present State of the Art
A phenomena called Acid Rain is damaging our ecological system. It is of great concern to the world's population. Acid rain is normally described as pollution that is washed from the air and deposited, along with the rainfall, upon the earth. Within the scientific community, acidity is measured and reported as pH. pH is defined as the negative logarithm of the hydrogen ion concentration. pH values range between 1 and 14. A pH of 1 is very acid, 7 is neutral and 14 is very caustic. Typical reported values for acid rain are in the 3.5 to 5 pH range. The National Bureau of Standards supplies reference material #2694 in pH of 4.30 and 3.59. Neutral pH 7 is not reached in normal rainfall due to carbonic acid generated by solution of carbon dioxide. Typical values for uncontaminated rainfall are in the 5.5 to 5.6 pH range. The acidic solutions have been shown to have a deleterious effect on all facets of mankind. These include lakes, streams, trees, vegetation and other facets of nature. Buildings, historic sites, exposed works of art etc are also suffering serious surface damage.
The acidity of precipitation is typically determined by collecting discrete samples of rainfall and measuring the pH with an appropriate electrode. In most studies bulk samples taken during a complete rainfall event are evaluated. The first portion of a rainfall event contains the bulk of the acidic components. Later rain falls through scrubbed air and is less acid. This follow-on rainfall greatly dilutes the acidity of the sample. These data serve well in evaluating damage to lakes and streams. Due to the great dilution, the value of the data in predicting damage to surfaces is of limited value. The collected rainfall samples are typically transferred to a distant laboratory for analysis. These samples change with time unless stringent measures such as preservative addition and cold storage are employed to maintain their integrity. The attendance of an operator is required after or during each rainfall event.
As the rain falls through the air, it not only scrubs the atmosphere of it's acidic components but also it's atmospheric dust. In many locations, this dust is quite basic. It reacts with the acid and partially neutralizes it. While this is not a factor in the study of the gross effects of acid rain, it reduces the value of the data for air quality management. It would be far better for the investigator to have the option of eliminating the effect of the atmospheric dust.
Rainfall events are relatively rare in the polluted world. This precludes continual monitoring of the acidic pollution of the atmosphere.